JP7431294B2 - Robot hand and robot hand control method - Google Patents

Description

The present invention relates to a robot hand and a method of controlling the robot hand.

Robot hands equipped with claws for gripping workpieces are known. Such a conventional robot hand is operated by setting a gripping force so as to grip a workpiece having a predetermined specific shape or material. However, when trying to grip various kinds of unspecified workpieces with conventional robot hands, there is a risk of damaging the workpieces if the gripping force of the claws is too strong for the material of the workpieces. If the force is too weak, the workpiece may fall while being gripped. As described above, with the conventional robot hand, it is difficult to grip various types of unspecified workpieces with appropriate gripping force without changing the gripping force setting according to the type of workpiece. In order to achieve control such as ``grasping hard workpieces firmly and gripping soft workpieces with minute force'' for various types of unspecified workpieces, a pressure sensor is installed on the robot hand to detect the gripping force. It may be possible to adjust the However, providing a pressure sensor increases manufacturing costs. On the other hand, there is a technique in which the deformation rate of the workpiece is obtained in advance by associating the displacement amount of the claw with the gripping force, and the gripping force of the claw is controlled according to this deformation rate (for example, see Patent Document 1).

JP2018-069381A

In order to obtain the deformation rate of the workpiece as described above, advance preparation is required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a robot hand and a control method for the robot hand that can grip various types of unspecified workpieces with an appropriate gripping force using a simple method without having to change the gripping force settings for each type. shall be.

The above object includes a motor, a plurality of claws that grip a workpiece according to the rotation of the motor, an encoder that detects a rotational position of the motor, and a plurality of claws that grip the workpiece according to the rotational position of the motor. a control device that controls the torque of the motor; the control device includes a limiting unit that executes a limiting process that limits the torque to a torque limit value or less; and a control unit that executes a limiting process that limits the torque to a torque limit value or less; an estimating unit that estimates that the claw has contacted the workpiece when the speed becomes equal to or less than a threshold; and an increasing process that gradually increases the torque beyond the torque limit value after the claw has contacted the workpiece. a calculation unit that calculates the amount of movement from the position where the claw contacts the workpiece to the current position based on the rotational position during the execution of the increase process; a maintenance unit that performs maintenance processing to maintain the torque when the torque becomes equal to or greater than a torque upper limit value that is larger than the torque limit value, or the torque when the movement amount becomes equal to or greater than a movement amount upper limit value; This can be accomplished by a robot hand, including.

Further, the above object is to execute a limiting process to limit the torque of a motor that drives a plurality of claws to grip a workpiece to a torque limit value or less, and to execute a limiting process to limit the torque of a motor that drives a plurality of claws to grip a workpiece, and to execute a limiting process to limit the rate of change in the rotational position of the motor during execution of the limiting process. becomes less than a threshold value, it is estimated that the claw has contacted the workpiece, and after the claw has contacted the workpiece, executing an increasing process of gradually increasing the torque beyond the torque limit value; During the execution of the increase processing, the amount of movement from the position where the claw contacts the workpiece to the current position is calculated based on the rotational position, and during the execution of the increase processing, the torque is lower than the torque limit value. This can also be achieved by a robot hand control method that executes a maintenance process that maintains the torque when the torque exceeds a large torque upper limit, or the torque when the movement amount exceeds a movement amount upper limit.

It is possible to provide a robot hand and a robot hand control method that can grip various types of unspecified workpieces with an appropriate gripping force using a simple method without having to change the gripping force for each type.

FIG. 1 is a schematic configuration diagram of a robot hand. FIG. 2 is a block diagram showing a schematic configuration of a control device for a robot hand. FIG. 3 is a flowchart showing an example of gripping control. FIG. 4 is a flowchart showing an example of the restriction process. FIG. 5 is a flowchart showing an example of the increase process. FIG. 6 is a timing chart showing changes in the position of the claw and the torque of the motor when gripping a soft workpiece. FIG. 7 is a timing chart showing changes in the position of the claw and the torque of the motor when gripping a hard workpiece.

FIG. 1 is a schematic configuration diagram of a robot hand 1. As shown in FIG. The robot hand 1 includes a control device 10, an encoder 20, a motor 30, a driving gear 40, a driven gear 50, and a claw 60. The control device 10 controls the operation of the robot hand 1 as a whole. The motor 30 is a drive source for opening and closing the claws 60, and is, for example, a stepping motor or a brushless DC motor. The encoder 20 is provided at the base end of the rotating shaft 32 of the motor 30, and detects the rotational position of the motor 30 (the rotation angle of the rotating shaft 32 of the motor 30). The encoder 20 may be optical or magnetic. The drive gear 40 is provided at the tip of the rotating shaft 32 of the motor 30, and meshes with the driven gear 50. The rotational force of the motor 30 is transmitted from the driving gear 40 to the driven gear 50 via the rotating shaft 32. The driven gear 50 has a substantially semicircular shape, and teeth are formed on an arcuate outer peripheral surface. The meshing mechanism between the driving gear 40 and the driven gear 50 is, for example, a worm gear, but it may also be a screw gear or another gear. A base end portion of the pawl 60 is fixed to the driven gear 50. Although only two pairs of driven gears 50 and pawls 60 are illustrated in FIG. 1, the present invention is not limited to this, and three or more pairs of driven gears 50 and pawls 60 may be provided.

As the motor 30 rotates in the forward direction, the driven gear 50 swings in one direction according to the engagement with the drive gear 40, and the tips of the claws 60 approach each other. When the motor 30 rotates in the opposite direction, the driven gear 50 swings in the opposite direction, which is the opposite of the one direction described above, and the tips of the claws 60 are separated from each other. By bringing the tips of the claws 60 closer to each other, it is possible to grip the workpiece to be gripped. Further, by separating the tips of the claws 60 from each other, the workpiece can be released. In this manner, the claws 60 can be opened and closed by switching the rotation of the motor 30 between forward rotation and reverse rotation.

FIG. 2 is a block diagram showing a schematic configuration of the control device 10. As shown in FIG. The robot hand 1 is used by being fixed to the tip of a robot arm. Further, the control device 10 controls the drive of the motor 30 in response to a command from a robot controller 100 that controls the entire operation of the robot hand 1 and the robot arm. Control device 10 includes a control section 11 and a driver circuit 13. The control unit 11 is mainly composed of a microcomputer, and internally includes a CPU, ROM, RAM, I/O, and a bus line connecting these components, all of which are not shown. Each process in the control unit 11 may be a software process in which a CPU executes a program stored in a physical memory such as a ROM (i.e., a readable temporary tangible recording medium), or Hardware processing may be performed using a dedicated electronic circuit using an FPGA (Field Programmable Gate Array) or the like.

The control unit 11 calculates the position and movement amount of the claw 60 based on the detection signal from the encoder 20. As mentioned above, the opening and closing of the pawl 60 is performed by transmitting rotational force from the driving gear 40 to the driven gear 50 by the rotation of the motor 30, so the opening and closing status of the pawl 60 can be obtained from the detection signal from the encoder 20. This is because it can be determined by the rotation angle of the rotating shaft 32. If the motor 30 is a stepping motor, the driver circuit 13 has a switching element that controls the energization of the coils of each phase, and drives the motor 30 by switching the energization of the windings of each phase of the motor 30. control. In the driver circuit 13, in addition to utilizing the function of a general-purpose IC for controlling the motor 30, a shunt resistor is provided and the potential difference is A/D converted. Thereby, the control unit 11 can grasp the current of the coils of each phase of the motor 30. Similarly, in the driver circuit 13, by using the function of a general-purpose IC for controlling the motor 30, it is possible to set the effective value of the energization of each phase of the coil of the motor 30 by modulating PWM or the like. . Furthermore, the control unit 11 can estimate the torque T of the motor 30 based on the current of the coils of each phase and the detection signal from the encoder 20. Further, as described above, the control unit 11 can control the current of the coils of each phase of the motor 30. Therefore, the control unit 11 can arbitrarily set the torque T by referring to the detection signal from the encoder 20 and setting the current of the coil of each phase of the motor 30. In this way, the control unit 11 can control the drive of the motor 30 and ultimately control the opening and closing of the pawl 60 by issuing a command to the driver circuit 13 based on the detection signal from the encoder 20. It is.

Next, gripping control executed by the control unit 11 of the control device 10 will be described. FIG. 3 is a flowchart showing an example of gripping control. The control unit 11 first executes a limiting process to limit the torque T of the motor 30 (step S10), then executes an increasing process to increase the torque T of the motor 30 (step S20), and then increases the torque T of the motor 30. A maintenance process for maintaining the torque T is executed (step S30). The restriction process will be explained below.

FIG. 4 is a flowchart showing an example of the restriction process. The control unit 11 acquires the target position Pt of the claw 60, the moving speed S of the claw 60, and the torque limit value Tr of the motor 30 based on the command from the robot controller 100 (step S11). Next, the control unit 11 issues a command to the driver circuit 13 to limit the current applied to the motor 30 so that the torque T of the motor 30 is constant below the torque limit value Tr (step S12), and while The motor 30 is controlled so that the motor 60 moves from the current position toward the target position Pt at a moving speed S (step S13). As a result, the claw 60 moves to close with a relatively weak torque T of the motor 30 that is less than or equal to the torque limit value Tr.

Next, the control unit 11 determines whether all the claws 60 have contacted the workpiece while the torque T of the motor 30 is limited (step S14). Specifically, it is determined whether the rate of change in the rotational position of the motor 30 (the amount of change in the rotation angle of the rotation shaft 32 per unit time) has become equal to or less than the threshold value α. The threshold value α is set to a value smaller than the rate of change of the rotational position of the motor 30 corresponding to the moving speed S described above. That is, it is determined whether the moving speed S has decreased to a moving speed corresponding to the threshold value α. The rate of change of the rotational position is calculated by the encoder 20 based on the amount of rotation of the motor 30 within a predetermined period of time. If the rate of change in the rotational position of the motor 30 is greater than the threshold value α, it is determined that all the claws 60 are not in contact with the workpiece yet. When the rate of change in the rotational position of the motor 30 decreases to below the threshold value α, it is determined that all the claws 60 have contacted the workpiece. If No in step S14, the process in step S13 is executed again. If Yes in step S14, the restriction process ends, and the above-described increase process is then executed.

Expansion processing will be explained. FIG. 5 is a flowchart showing an example of the increase process. The control unit 11 obtains the torque upper limit value Tmax and the movement amount upper limit value ΔPmax (step S21). As the torque upper limit value Tmax and the movement amount upper limit value ΔPmax, those stored in advance in the above-mentioned ROM may be used, or numerical values transferred from the robot controller 100 may be held in the above-mentioned RAM and used. The torque upper limit value Tmax is a value larger than the torque limit value Tr. Next, the control unit 11 temporarily stores in the memory the contact start position P1 where it is determined that all the claws 60 have contacted the workpiece in the restriction process (step S22). Next, the control unit 11 increases the torque T by one step (step S23). Specifically, the control settings are changed in accordance with the control characteristics of the motor employed as the motor 30 so that the torque increases. For example, the absolute value of the current in each phase coil of the motor 30 may be increased, or the duty ratio of PWM control may be increased. Here, "increase by one step" means to discretely increase the torque T of the motor 30, and the torque T fluctuates before and after the increase, resulting in the above-mentioned meshing mechanism of the drive gear 40 and the driven gear 50. This means that a large amount of energy is transmitted from the motor 30 to the drive gear 40 with respect to friction loss. In a meshing mechanism, if the meshing speed decreases, there is a risk that the meshing will stop due to friction loss. Specifically, the friction that was acting up until then changes from dynamic friction to static friction, and since the static friction is greater than the dynamic friction, there is a risk that the meshing mechanism may become stuck, so to speak. In order for the meshing mechanism to start moving again, a torque impact is applied to the meshing mechanism by increasing the torque T in a discrete value, thereby making it possible to transition from static friction to dynamic friction.

Next, the control unit 11 determines whether the torque T is greater than or equal to the torque upper limit value Tmax (step S24). If YES in step S24, the increase process ends, and a maintenance process is executed to maintain the current torque T of the motor 30 at the torque upper limit value Tmax (step S30).

If No in step S24, the control unit 11 temporarily stores the current position P2 of the claw 60 in the memory (step S25). Next, the control unit 11 calculates the movement amount ΔP of the claw 60, which is the difference between the contact start position P1 and the current position P2 (step S26). Next, the control unit 11 determines whether the calculated movement amount ΔP is greater than or equal to the movement amount upper limit value ΔPmax (step S27). If No in step S27, the process in step S23 is executed again. In this case, the torque T is further increased by one step in step S23. As a result, as long as the determination is No in steps S27 and S24, the torque T increases at a constant increase rate. If YES in step S27, the main increase process ends, and a maintenance process for maintaining the current torque T of the motor 30 is executed (step S30).

Next, the transition of the position P of the claw 60 and the torque T of the motor 30 when gripping a workpiece will be explained. FIG. 6 is a timing chart showing changes in the position P and the torque T of the motor 30 when a soft workpiece is gripped. At time t0, the torque T is maintained substantially constant at a torque T0 that is less than the torque limit value Tr, and the position P of the pawl 60 gradually moves from the initial position P0. At time t1, the position P of the claws 60 reaches the contact start position P1 where all the claws 60 come into contact with the workpiece. Since the position P of the pawls 60 does not move, when it is determined that all the pawls 60 have contacted the workpiece at time t2, the torque T increases and the position P of the pawls 60 begins to move. When the movement amount ΔP, which is the difference between the current position P2 and the contact start position P1, reaches the movement amount upper limit value ΔPmax at time t3, the torque T is maintained at the torque T1 at that time. In this way, a soft workpiece can be gripped with a weak gripping force that does not cause damage.

FIG. 7 is a timing chart showing changes in the position P of the claw 60 and the torque T of the motor 30 when gripping a hard workpiece. Similar to the case shown in FIG. 6, after times t0, t1, and t2, the torque T increases, but the current position P2 does not move from the contact start position P1. Therefore, the torque T further increases, and at time t3, the torque T reaches or exceeds the torque upper limit value Tmax, and the torque T is maintained at the upper limit value Tmax. In this way, it is possible to grip a hard workpiece with a strong enough gripping force to prevent it from falling.

The above-mentioned restriction processing (step S10) will be supplemented here. The gist of the restriction process is to detect the location of the workpiece, in other words, to control the claw 60 to detect the presence of the workpiece. Torque T is set to a relatively weak value so as not to damage the workpiece in order to detect the position of the workpiece. On the other hand, if the torque T is weakened (lower value), the rotational speed of the motor 30 will become slower depending on the type and control method of the driver circuit 13 employed, or the type of motor 30 employed, making it difficult to detect the position of the workpiece. It may take some time. In order to avoid such inconveniences, the motor 30 is operated in a high-speed rotation and low-torque control region during limit processing, and the motor 30 is operated in a low-speed rotation and high-torque control region during increase processing and maintenance processing. You can also choose to do so. For example, if an internal rotor brushless DC motor is used as the motor 30, this can be achieved by switching the connections of the stator windings and changing the excitation of the poles. Furthermore, if the motor 30 is equipped with a transmission (not shown) that can change the gear ratio and the ratio between the rotational speed of the motor 30 and the rotational speed of the drive gear 40 can be changed, the motor 30 is It is also possible to rotate the motor 30 at high speed rotation and low torque with a low reduction ratio, and to rotate the motor 30 at low speed rotation and high torque with a high reduction ratio during the increase processing and maintenance processing.

As described above, in order to handle various types of unspecified workpieces, the gripping force setting for each type of workpiece can be changed, the deformation rate of the workpiece can be obtained in advance, and the motor 30 detected by the encoder 20 can be adjusted. There is no need for a pressure sensor or the like to measure the gripping force based on the rotational position. Therefore, the workpiece can be gripped with an appropriate gripping force depending on the hardness of the workpiece using a simple method.

Due to the features of the embodiment described above, a robot to which the robot hand of this embodiment is applied has the following advantages. First, a single robot hand can dynamically handle a wide variety of unspecified types of workpieces. Therefore, the man-hours required for teaching and setup changes when building a mass production line can be reduced. Furthermore, after determining the gripping force for each workpiece through the increasing process, the torque T and the amount of movement ΔP can be obtained. Therefore, for example, in a production line where the same type of workpieces are continuously passed, the robot hand of this embodiment can be used as a measuring instrument as well as gripping the workpieces. Thereby, the torque T and the amount of movement ΔP after determining the gripping force can be regarded as the physical properties of each workpiece, and it is possible to statistically judge the quality of the workpiece and to identify non-standard workpieces. As a similar application, in a production line where a plurality of types of workpieces are continuously passed, it is also possible to separate the workpieces based on the torque T and the amount of movement ΔP after the gripping force is determined.

As mentioned above, in addition to the torque T and the amount of movement ΔP obtained at the time of determining the gripping force of each workpiece in the increasing process, the position P1 of the claws when it is determined that all the claws have contacted the workpiece in the limiting process, The time required for the movement amount ΔP to exceed the movement amount upper limit value ΔPmax (t3−t2) also represents the physical properties of each workpiece. These plural physical quantities representing the physical properties of each workpiece are taken as gripping parameters. By using this gripping parameter, the robot hand of this embodiment can be widely used. In the case of a production line where the same type of workpieces are continuously passed as described above, a threshold value is set that defines the range of good products in order to judge whether the workpieces are good or bad, and the gripping parameters obtained by gripping each workpiece are compared with this threshold value. This allows defective products to be detected with high accuracy. In addition, a plurality of non-defective workpieces are prepared in advance to serve as standards for pass/fail judgment, and the workpieces in this group of non-defective products are continuously gripped to obtain gripping parameters and subjected to statistical processing to define the range of non-defective products. Generate a threshold. Thereby, defective products can be detected by comparing the gripping parameters of each workpiece with this threshold value during subsequent operation of the production line. Furthermore, since the production line process designer does not need to handle the gripping parameters as specific numerical values, input errors and work man-hours can be reduced, leading to labor savings.

The aforementioned acquisition of gripping parameters, generation of thresholds, and comparison of gripping parameters and thresholds may be performed by the control unit 11, or the necessary information may be exchanged with an external robot controller 100 or the like and communicated with other robot hands. It may also be executed comprehensively.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and modifications and changes may be made within the scope of the gist of the present invention as described in the claims. It is possible.

1 Robot hand 10 Control device 20 Encoder 30 Motor 32 Rotating shaft 40 Drive gear 50 Driven gear 60 Claw

Claims (4)

motor and
a plurality of claws that grip the work according to rotation of the motor;
an encoder that detects the rotational position of the motor;
a control device that controls the torque of the motor so that the claw grips the workpiece according to the rotational position,
The control device includes:
a limiting unit that executes a limiting process to limit the torque to a torque limit value or less;
an estimation unit that estimates that the claw has contacted the workpiece when the rate of change of the rotational position becomes equal to or less than a threshold while executing the restriction process;
an increasing unit that executes an increasing process of gradually increasing the torque beyond the torque limit value after the claw contacts the workpiece;
a calculation unit that calculates a movement amount from a position where the claw contacts the workpiece to a current position based on the rotational position during execution of the increase processing;
During execution of the increase process, if the torque becomes equal to or greater than the torque upper limit value, which is larger than the torque limit value, before the movement amount becomes equal to or greater than the movement amount upper limit value, the torque upper limit value is maintained, and the If the amount of movement becomes equal to or greater than the upper limit value of movement before the torque becomes equal to or more than the upper limit of torque during the execution of the increase process , A robot hand, comprising: a maintenance section that performs maintenance processing to maintain the torque. The robot hand according to claim 1, wherein the limiting section maintains the torque at a constant value equal to or less than the torque limit value in the limiting process. The robot hand according to claim 1 or 2, wherein the increasing section increases the torque at a constant increase rate. Executes a limiting process to limit the torque of the motor that drives multiple jaws to grip the workpiece to a torque limit value or less,
If the rate of change in the rotational position of the motor becomes less than or equal to a threshold during execution of the restriction process, it is estimated that the claw has contacted the workpiece;
performing an increasing process of gradually increasing the torque beyond the torque limit value after the claw contacts the work;
calculating the amount of movement from the position where the claw contacts the workpiece to the current position based on the rotational position during the execution of the increase processing;
During execution of the increase process, if the torque becomes equal to or greater than the torque upper limit value, which is larger than the torque limit value, before the movement amount becomes equal to or greater than the movement amount upper limit value, the torque upper limit value is maintained, and the If the amount of movement becomes equal to or greater than the upper limit value of movement before the torque becomes equal to or more than the upper limit of torque during the execution of the increase process , A method for controlling a robot hand, which performs a maintenance process to maintain the torque.

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